Compatibility: Win 3.0+

See: 4000H (srvc: enable VM-assisted video save/restore)

4001H (ntfy: about to switch to background)
4002H (ntfy: about to switch to foreground)

4003H (srvc: enter critical section)
4004H (srvc: exit critical section)

4005H (ntfy: saving video registers)
4006H (ntfy: restoring video registers)

4007H (srvc: disable VM-assisted save/restore)

Notes:   These functions are used by programs which expect to be run in
virtual machines under Enhanced-Mode Windows.

They provide access to some Virtual Display Device (VDD)
services and notifications to help them manage the screen as
they are swapped into and out of the foreground.

In general, these fns are used only by programs which do weird
stuff to the video display; for instance, programs which
display in video modes which are not supported by the VDD or
perform on-the-fly modifications to on-screen fonts, etc.

  The services are tools that can be called by VM-aware
applications to access services provided by the VDD.

  The notifications represent INT 2fH fns that are invoked by the
Windows VDD.  To receive these notifications, VM-aware
applications can intercept INT 2fH and watch for AX=40xxH.

- -

INT 2fH 40xxH: Virtual Display Driver Functions